1. Field of the Invention
The invention relates to an apparatus for mechanically joining metal sheets, which lie flat one upon the other.
In the case of mechanical joining by means of deformation, small three-dimensional formations are formed on sheet-metal parts, which are to be connected at connecting locations, under the action of tool sets, which each comprise a punch and die, said three-dimensional formations being the joining elements. These joining elements are formed in that, in a joining region, the sheet-metal material of the sheet-metal parts, which lie flat one upon the other, is jointly displaced out of a sheet-metal plane and upset. This is also referred to as clinching.
2. Description of the Background Art
A joining tool which can be used for this purpose is known, for is example, from EP 0 077932 B1. In this document, a joining region is bounded by a press-driven punch and a stationary die. If the punch is moved in the direction of the die the material of the metal sheets is deep-drawn in a cavity of the die. If the die-side metal sheet reaches the base of the cavity, which is formed by an anvil, and if the pressure on the punch is maintained or increased, the base of the press-joined joining section may spread out laterally since the material is upset and the walls which bound the die cavity laterally yield. It is also known, from EP 0 366 987 A1, that, in the case of such a joining tool, the punch has a stop which limits its penetration depth. The penetration-depth limitation, and thus a displacement-limiting means, of the punch ensures that the joining is not subjected to excessive stressing. However, it has proven disadvantageous that the known displacement-limiting means is fixed and subjects the joining tool to mechanical loading.